The lady of the rings: Integrative systematics of <i>Nanuca</i> Er. Marcus, 1957 (Mollusca: Nudibranchia: Myrrhinidae) reveals a hidden diversity

Abstract Myrrhinidae are one of the most species-rich families of aeolid nudibranchs. The genus Nanuca comprises a single species, N. sebastiani, which has a wide geographical distribution along the tropical Western Atlantic. The taxonomy of Nanuca has not been thoroughly studied, and its relationship with the genus Dondice is unclear. Using newly generated sequences, we created the most comprehensive dataset to date for studying evolution of Myrrhinidae. We employed an integrative approach combining phylogenetic analyses and species’ delimitation methods (ABGD, ASAP, GMYC, PTP) with mitochondrial (COI, 16S) and nuclear (28S LSU D1-D2) genes, as well as morphological and biogeographical evidence. Our analysis recovered the six genera of Myrrhinidae as monophyletic, reinforcing Dondice and Nanuca as distinct taxa. Molecular phylogenetics, species’ delimitation, and morphological data support the existence of six species of Nanuca: the polymorphic N. sebastiani and five new pseudocryptic species, N. smaugi sp. nov., N. perolata sp. nov., N. cahuitaensis sp. nov., N. alboviridis sp. nov., and N. leali sp. nov. Our work sheds light on biogeographic barriers, like the Amazon River plume, and ecological transitions along Florida, the Caribbean Sea, and Brazil as drivers to Nanuca diversification. Our findings highlight the importance of considering nudibranch species’ diversity within an evolutionary context.